Question

find the length of 13.2 kg of copper wire of diameter 4mm ,when 1 cubic cm of copper weighs 8.4g

Answer 1

Let its length be l. 
A wire is in the form of cylinder. 
R=2mm=0.2cm 
Volume=(22/7) (0.2)^2 (l) 
Now 1cc --- 8.4g 
(22/7) (0.2)^2 (l)cc----(8.4) (22/7) (0.2)^2 (l) 
Now just equate it to 13200g 

Then,l=12500cm=125m.